The impact of co-treatment with graphene oxide and metal mixture on Salmo trutta at early development stages: The sorption capacity and potential toxicity

Abstract

Graphene oxide (GO) are novel nanomaterials with a wide range of applications due to their high absorption capacity. This study was undertaken with a view to assess the bioaccumulation and acute toxicity of GO used in combination with the heavy metal mixture (Cr, Cu, Ni and Zn) to fish embryos and larvae. For this purpose, Salmo trutta embryos and larvae were subjected to the 4-day long treatment with three different concentrations of GO, the metal mixture, which was prepared of four metals at the concentrations corresponding to the maximum-permissible-concentrations for EU inland waters (Cr-0.01, Cu-0.01, Ni-0.034, and Zn-0.1 mg/L), and with GO in combination with MIX (GO+MIX). When used in combination with the metal mixture, GO exhibited a high metal sorption capacity. The obtained confocal fluorescence microscopy results showed that GO located in the embryo chorion causing its damage; in larvae, however, GO were found only in the gill region. Results of these experiments confirmed the hypothesis that GO affects the accumulation of metals and mitigates their toxic effects on organism. In embryos, the acute toxicity of exposure to GO and co-exposure to MIX+GO was found to manifest itself through the decreased heart rate (HR) and malondialdehyde (MDA) level and through the increased metallothionein (MT) concentration. Meanwhile, in larvae, GO and MIX+GO were found to induce genotoxicity effects. However, changes in HR, MDA, MT, gill ventilation frequency, yolk sack absorption and cytotoxicity compared with those of the control group were not recorded in larvae. The obtained results confirmed our hypothesis: the combined effect of MIX and GO was less toxic to larvae (especially survival) than individual effects of MIX components. However, our results emphasize that fish exposure to GO alone and in combination with heavy metal contaminants (MIX+GO) even at environmentally relevant concentrations causes health risks that cannot be ignored.

Keywords: Accumulation; Biological parameters; Combined effects; Contamination with heavy metals; Fish embryos and larvae; Nanosorbents.